The Phantom Pain uses the same in-game currency system as Metal Gear Solid: Peace Walker, called Gross Military Product, or GMP. Similar to Peace Walker, GMP is used in The Phantom Pain to build up your base.

Speculation says that the PSN requirement, combined with the reveal of "optional in-game purchases" on the game's store page, could indicate the use of real money for certain features relating to Mother Base, like buying GMP, but nothing has officially been confirmed by Konami.

For now, we've reached out to Konami for clarification and will report back as soon as we have more information.

Chloi Rad is a Staff Writer for IGN. You can follow her on Twitter at @_chloi.